1. Field of the Invention
The present invention relates in general to power seat slide devices, and more particularly, to power seat slide devices of a so-called "belt-in" type used for an automotive seat which has a seat belt anchored to a rear end portion thereof.
2. Description of the Prior Art
Power seat slide devices widely used nowadays are of a type which comprises generally a rack fixed to a stationary rail, a pinion meshed with the rack and operatively held by a movable rail which is slidably disposed on the stationary rail, and an electric motor for driving the pinion through a flexible wire. When the motor is energized, the pinion is driven and thus moves the movable rail on and along the stationary rail. With this, the seat mounted on the movable rail is moved to a desired fore-and-aft position.
In case of the "belt-in" type, the movable rail has at its rear end a belt anchor portion to which an end of a seat belt is fixed. Thus, upon a vehicle collision, a big stress is suddenly applied to the belt anchor portion of the movable rail by a belt wearer on the seat. This requires the necessity of assuring the locked connection between the movable and stationary rails. In fact, if the locked connection is poor, the movable rail may get off the stationary rail upon the vehicle collision. Of course, this is very dangerous.
In order to solve such dangerous phenomenon, the same inventors have proposed a measure which is disclosed in Japanese Patent First Provisional Publication 64-60445.
As is shown in FIG. 7 of the accompanying drawings, in the measure of the publication, the stationary rail is constructed of two overlapped elongate members, which are a first elongate stationary rail member 1 having somewhat raised side flanges 1A and a second elongate stationary rail member 2 having a generally C-shaped cross section. The movable rail is constructed of two overlapped elongate members, which are a first elongate movable rail member 3 having embracing side portions which slidably embrace the side flanges 1A of the first elongate stationary rail member 1 and a second elongate movable rail member 4 having embracing side portions which slidably embrace the side wall portions of the second elongate stationary rail member 2.
Upper and lower case members 5 and 6 are connected to the movable rail in a manner to put therebetween the stationary rail.
The two-ply stationary rail is formed with an axially extending slot 1B. One side edge of the slot 1B is formed with a plurality of teeth 1C. A pinion 8 is meshed with the teeth 1C and is rotatably carried by the upper and lower case members 5 and 6 through a pinion shaft 7.
With the robust construction possessed by the two-ply stationary rail and the fully embracing type movable rail, the dangerous phenomenon, viz., the disengagement of the movable rail from the stationary rail, is suppressed.
However, this time, the power seat slide device of the publication has the following drawbacks.
That is, first, the robust construction of the stationary and movable rails causes results in an increase in production costs of the seat slide device. Furthermore, because of necessity of structural precision, the lower case member 6 must be constructed of die casting, which promotes the cost increase. Furthermore, for the purpose of assuring the meshed engagement between the pinion 8 and the teeth 1C of the two-ply stationary rail, it is necessary to enlarge the size of the pinion 8 to a certain degree. However, this causes bulky and heavy construction of the seat slide device.